Brandishing signs reading “The future is female” and “Make America kind again,” tens of thousands of women in a sea of pink hats marched on the nation’s capital Saturday, raising their voices in direct opposition to Donald Trump.

As Trump attended a prayer service at the Washington National Cathedral on his first full day as president, protesters from across the country descended on D.C., arriving in buses, caravans and packing public transportation to gather near the National Mall and hear from prominent women’s rights activists, lawmakers and celebrities. A slow-moving procession began Saturday afternoon along Constitution Avenue toward the Washington Monument, and planned to end near the White House.

Organizers say the Women’s March on Washington was intentionally scheduled for the day after the presidential inauguration with the aim of sending a powerful message to the newly minted administration: Women’s rights are human rights.

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Demonstrators arrive at Union Station for the Women’s March on Washington on Jan. 21, 2017, in Washington, DC. Jessica Kourkounis / Getty Images